Tsunami

Coming from the Japanese word 'harbour wave', tsunami are a series of waves – with wave lengths up to hundreds of kilometres between crests - caused by undersea seismic disturbances.

Causes of tsunami

Ground displacement (movement) due to undersea earthquakes is the most common cause of tsunami. However, they may also be caused by submarine landslides, volcanic eruptions and caldera collapses, and even large meteorite impacts.

Tsunami may travel across entire ocean basins. For example, an earthquake in South America could trigger a tsunami that could severely impact New Zealand.In the open ocean, a tsunami wave may only be a matter of centimetres high. Its height increases as it approaches shore and slows down, due to the water depth becoming shallower. Tsunami waves can be several to tens of metres high when they hit the shore.

Potential consequences of tsunami

Tsunami can cause serious flooding of coastal areas. Large tsunami may inundate many kilometres inland.

The waves which initially hit the coast, followed by flooding spreading inland, can cause serious damage to infrastructure (including buildings and roads), land, crops and livestock. They can also result in injury or loss of human life. Strong currents may also cause damage to ships and coastal infrastructure.

Incidences of tsunami in recent years

2011 Tohoku Tsunami - The Tohoku Tsunami took place on March 11, 2011, and was caused by a magnitude 9 megathrustearthquake approximately 32 km deep and 72 km off the east coast of the Oshika Peninsula of Tohoku, Japan (the fourth biggest earthquake since records began). The tsunami waves generated reached 10 m in height, and in some cases washed up to 10 km inland. This tsunami had an impact over the whole Pacific with parts of the west coast of North and South America being hit by waves up to 3 m high

2010 Chilean Tsunami - The Chilean Tsunami was caused by a magnitude 8.8 earthquake of the coast of the Maule/Biobío Region in February 2010 (the sixth biggest earthquake since records began). The tsunami caused deaths in Chile and a tsunami watch across the entire Pacific Ocean.

2009 Samoa Tsunami - The Samoan Tsunami was triggered by a magnitude 8.1 outer rise earthquake on the Tonga-Kermadec Subduction zone, in September 2009. Tsunami waves inundated parts of Samoa, American Samoa and Tonga causing the loss of 189 lives in these three countries.

2004 Sumatra/Boxing Day Tsunami - The Indian Ocean (Boxing Day) Tsunami was triggered by a massive (magnitude 9.1) megathrust earthquake off the coast of Sumatra, Indonesia (the third biggest earthquake since records began). It affected not only Indonesia but also Thailand, Sri Lanka, India and the Maldives, and caused over 230,000 deaths.

Tsunami research at NIWA

New Zealand is at risk from tsunami due to its long coastline and its position on the Pacific Rim of Fire. Steep undersea canyons such as the Kaikoura Canyon and the Cook Strait Canyon are also areas of potential submarine landslides which can cause dramatic local tsunami.NIWA's research into this natural hazard covers underwater earthquake faults and landslides, tsunami propagation and inundation modelling, post-disaster surveys and risk/loss assessment.

Current NIWA research projects

Underwater earthquakes/landslides - NIWA scientists are engaged in better understanding the risk that undersea earthquakes and landslides could pose to New Zealand's coastal communities, by mapping the offshore faults and possible landslide sites.

Modelling tsunami propagation and inundation using the Gerris and RiCOM models:

Gerris - Gerris is based on a square grid that may be refined by subdividing any given square into 4 subsquares.

RiCoM - RiCOM is based on a triangular mesh, by varying the triangles size slightly with each one it can grade smoothly between different sizes.

RiskScape (risk and loss assessment) - Data collected from post-disaster surveys is fed into risk and loss assessment models: the more accurately costs can be calculated, the better the decisions around risk-reduction initiatives can be. Such information can also be used by areas at risk to help them better prepare for tsunami.NIWA and GNS Science have developed RiskScape, a software tool which enables users to analyse the risks and impacts of a range of hazards, including tsunami.In addition, recorded impacts be used to help refine computer models of how tsunami waves propagate and interact with coastal areas.

Post-disaster surveys - Teams of scientists, including NIWA researchers, undertake reconnaissance missions to areas affected by tsunami (and other hazards, e.g. tropical cyclones) to assess their impacts. These surveys are used to collect the data which inform risk and loss assessment models, and refine models of how tsunami waves behave.

Contact

RiCOM grid coloured according to depth. In deeper water larger triangles can be used. In shallower areas, especially those with complex coastline, the grid grades to smaller triangles for finer resolution. Solid colours in the figure indicate where the triangles are so fine that they blend together.